INTRODUCTION

WE-NET (World Energy Network), a part of "New Sunshine Project", which is a Japanese government sponsored program through New Energy and Industrial Technology Development Organization (NEDO) aimed at solving energy and environmental problems in the world. "Hydrogen Combustion Turbine", which is a subtask of WE-NET has been investigated under contracts with Japan Power Engineering and Inspection Corporation (JAPEIC) and Central Research Institute of Electric Power Industry (CRIEPI) for 4 years from 1993. The hydrogen combustion turbine cycle used for industrial power plant with the bigger power capacity has never realized in the world. The prototype plant with the power capacity of 50MW is going to be produced and operated by 2020. Hydrogen storage system and transportation system are also going to be prepared simultaneously. It is effective to reduce greenhouse gases by no generation of CO2. The fossil fuel like natural gases and oils is not infinite. Therefore, it is possible to be adopted to the industrial power plant in the near future.
In 1994, three different closed hydrogen combsution turbine cycles were evaluated. These are the Topping Extraction Cycle (A) (Jericha et al. 1989), the Bottoming Reheat Cycle (B) and Rankine Cycle(C). Results of this study showed the Topping Extraction Cycle (A) to be the best cycle (Sugishita, 1996).
Furthermore, the Topping Recuperation Cycle (D) was designed to be a highly efficient and highly feasible cycle suitable for high combustion temperature (1700C) (NEDO, 1996).
Subsequent to this research, the Closed Circuit Cooled Topping Recuperation Cycle (E) whose high temperature turbine is cooled by steam was designed to be more efficient than the above mentioned cycles. (NEDO, 1997)
This paper presents the summary of the system configurations of the above mentioned cycles.

CYCLE CONFIGURATIONS

The cycles (A), (B), (D) and (E) are a kind of gas turbine combined cycle whose working fluid is steam. The topping cycle is closed Brayton cycle and the bottoming cycle is Rankine Cycle. The topping cycle of the cycles (A), (B), (D) and (E) shown in Figure 1 are composed of low pressure compressor (LPC) 1, high pressure compressor (HPC) 2, HHT 4, heat exchanger 5, 6, and combustor 3. In the cycle (B), a combustor is added to the bottoming cycle of cycle (A) . In cycle (D), the heat exchanger 14 and 15 are added to cycle (A) to improve the thermal efficiency by recuperating the heat from the exhaust of HTT 4 to the inlet of combustor 3. In cycle (E), the closed circuit cooled system are applied to HHT 4 of cycle (D) to improve the thermal efficiency to reduce the excergy loss generated by the cooling fluid.

CYCLE PERFORMANCES

Cycle calculations are carried out to estimate the cycle performances of the above mentioned cycles. The typical calculation results of cycle calculations are shown in Table 1. The thermal efficiency of cycle (E) is 61.8% HHV, which is the highest thermal efficiency in all investigated cycles.
FEATURE OF CYCLES
Cycle (E) includes the heat exchanger to recuperate the heat from the outlet of HTT 4 to the inlet of combustor 3 and the closed circuit cooling system. This recuperation has benefits as follows;
o Increase the thermal efficiency in the feasible HTT inlet pressure of less than 50.
o Higher thermal efficiency in the range of more than 1500C.
o Higher first stage turbine vane height of HTT. It is easier to construct the complicated cooling passage inside of vanes and blades and higher aerodynamic efficiency of HTT.
Therefore cycle (E) is judged to be the most suitable cycle for hydrogen combustion turbine used for industrial power plant.

CONCLUSIONS

(1) The Closed Circuit Cooled Topping Recuperation Cycle (E) has the highest thermal efficiency of 61.8%(HHV).
(2) Cycles (D) and (E) have the biggest first stage turbine vane height of 85mm, it is easier to construct the complicated cooling passages inside of vanes and blades and higher aerodynamic efficiency of HTT.
(3) Cycle (E) is suitable the highly efficient and highly feasible hydrogen combustion turbine used for industrial power plant from the point of view of the thermal efficiency and the feasibility of components.